Study Guide

• Chemotrophs


  Organisms that gain their energy from chemical reactions, not light
• Autotrophs


  Organisms that absorb carbon dioxide and convert it into complex organic compounds
• Heterotrophs


  Organisms that obtain their carbon as carbon-based complex compounds by eating food
• Phototrophs

  • Trees in the elfin forests on Dominica
  • Sugar cane in fields on Barbados
  • Algae on coral reefs around St Kitts
  • Mangrove trees in Belize
  • Seagrass in the waters throughout the Caribbean
• Humans obtain their energy from food, which comes directly or indirectly from plants, which in turn absorb light energy from the Sun
• Photoautotrophs


  Plants, some prokaryotes, and some protoctists that absorb light energy for photosynthesis and fix carbon to make energy-rich organic compounds
• Chemoautotrophs


  Bacteria that harness energy from simple chemical reactions using highly reduced compounds, and use the energy released to fix carbon
• On the ocean floor are vent communities that flourish at depths far below that to which light reaches, and rely on chemoautotrophic bacteria
• Ways heterotrophs feed


  • Grazing plants
  • Preying on animals
  • Parasitising other organisms
  • Eating dead and decaying organisms
• Heterotrophs bite, chew, suck or filter to get their food, and most digest it
• Autotrophs


  Organisms that use simple inorganic compounds to make complex organic compounds, most use light energy to drive the anabolic reactions in which they make biological molecules
• Heterotrophs


  Organisms that use complex organic compounds to obtain the energy and biological molecules that they need
• Photosynthesis


  The absorption of light energy that is used to drive the synthesis of simple carbohydrates
• Respiration


  The transfer of energy from complex organic compounds to ATP and heat
• All organisms respire, except viruses which rely on the respiration of their host cells to be reproduced
• Sources of energy and carbon for organisms

  • Photoautotrophic (photosynthetic bacteria, some protoctists including algae, plants)
  • Photoheterotrophic (purple non-sulphur bacteria)
  • Chemoautotrophic (nitrifying bacteria)
  • Chemoheterotrophic (many bacteria, many protoctists, all fungi and all animals)
• Photosynthesis and respiration are not opposites of one another
• The deepest vent communities were found in 2010 in the Cayman Trench between Jamaica and Cuba
• Energy is the ability to do work and is measured in joules
• Energy is neither created nor destroyed, it is transferred (First Law of Thermodynamics)
• Energy flows, it does not cycle
• Uses of energy in organisms

  • Active transport
  • Movement
  • Biosynthesis - production of biological molecules
  • Raising energy levels of compounds so they take part in reactions
  • Growth and reproduction
  • Maintenance of body temperature in endotherms
• ATP


  The universal energy currency within cells in all organisms
• ATP structure


  A phosphorylated nucleotide, with adenine, ribose and phosphate groups
• ATP production


  1. Substrate-linked phosphorylation

  2. Chemiosmotic phosphorylation
• Oxidation/reduction reactions


  Involved in ATP production
• Roles of ATP in cells

  • Binding to proteins for movement
  • Binding to carrier proteins for active transport
  • Binding to inactive enzymes to activate them
  • Binding to enzymes so reactions can take place
  • Transferring a phosphate group to a molecule to increase its reactivity
  • Transferring enough energy to provide activation energy for most reactions in cells
  • Transferring AMP to a molecule to increase its reactivity
• ATP is not stored, it is produced by cells when they need it
• ATP is not transported between cells, it is produced locally
• ATP does not have 'high-energy bonds', the energy comes from the whole molecule
• ATP is not a high-energy compound, it has an intermediate energy level
• Leaves


  • Adapted for absorbing light, obtaining carbon dioxide, producing sugars in photosynthesis, exporting sugars and amino acids, importing water and ions, providing support to present a large surface area to light
• Leaf tissues and functions


  • Upper epidermis (secretes waxy cuticle, transparent to allow light)
  • Palisade mesophyll (contain many chloroplasts to absorb light)
  • Spongy mesophyll (allow diffusion of carbon dioxide)
  • Xylem (supply water and ions)
  • Phloem (transport assimilates away from leaf)
  • Lower epidermis (contain guard cells that control stomata)
• Upper epidermis


  Transparent to allow light to pass through to the mesophyll; may have stomata
• Palisade mesophyll


  • Cells contain many chloroplasts to absorb maximum light; large vacuole pushes chloroplasts to the edge of each cell; cells are cylindrical and at right angles to epidermis to reduce scattering of light by cell walls
• Spongy mesophyll


  • Cells separated by larger air spaces than in palisade mesophyll to allow diffusion of carbon dioxide throughout the leaf; air spaces also act as a store of carbon dioxide when stomata are closed
• Xylem


  Xylem vessels supply water and ions; water passes from xylem along cell walls of mesophyll cells and is then absorbed by individual cells by osmosis
• Phloem


  Phloem sieve tubes transport assimilates, such as sucrose and amino acids, away from the leaf to other parts of the plant
• Lower epidermis


  Cells are like those of the upper epidermis; some are specialized as pairs of guard cells that control the aperture of stomata through which carbon dioxide and oxygen diffuse in and out and water vapour diffuses out
• The leaves of most dicotyledonous plants have more stomata on the lower surface than on the upper. Many have none at all on the upper epidermis. However, leaves that float on water have almost all their stomata on the upper surface.